Heat-shock proteins 70 kDa and 19 kDa are not required for induction of embryogenesis of Brassica napus L. cv. topas microspores

It is currently accepted that 'stress' triggers induction of microspore embryogenesis, and for Brassica napus L. cv. Topas it is heat-shock. It has been postulated that the heat-shock proteins (HSPs) generated during heat stress have a central role in the induction mechanism. To test this hypothesis we developed a microspore induction procedure, using colchicine instead of heat treatment. The level of HSP70 increased significantly during and following the microspore heat treatment while sHSP19 expression was induced at the onset of heat-shock and declined after 8 h. In contrast, induction of embryogenesis with colchicine was not accompanied by elevation of HSP70 nor by induction of sHSP19, indicating that these HSPs are not required for induction of microspore embryogensis in this model system. These data refute the current hypothesis that HSPs have an essential role in triggering microspore embryogenesis.